1. Field of the Invention
The invention relates to a vehicle controller that includes a transmission coupled to the output of a power engine and capable of changing the gear ratio and the shift mode by using a continuously variable transmission and a gearshift mechanism.
2. Description of the Related Art
Conventionally, belt-type and traction-type (toroidal-type) transmission mechanisms are known as a continuously variable transmission mechanism for use in a vehicle transmission. These continuously variable transmission mechanisms transmit the torque by using the friction force between a transmitting member such as belt and power roller and a rotor such as pulley and disc, shearing force of an oil film, and the like, in order to continuously vary the gear ratio. This restricts the transmittable torque, reduces the power transmission efficiency when the gear ratio is large or small, and also limits a practically applicable gear ratio.
Conventionally, the transmission is not constructed using a continuously variable transmission mechanism alone but is constructed using combination of a continuously variable transmission mechanism and a gear mechanism such as a planetary gear mechanism. One example of such a transmission is described in JP-A-11-504415. The example of the transmission described in this publication will be described briefly. A driving pulley of the continuously variable transmission mechanism is coupled to the engine, and a driven pulley thereof is coupled to a sun gear of the planetary gear mechanism. A ring gear, which is arranged concentrically with the sun gear, is coupled to the output shaft of the transmission. A carrier holding a pinion gear meshed with the sun gear and the ring gear is coupled to the input shaft of the transmission through the gear mechanism and a clutch. In order to integrally rotate the whole planetary gear mechanism, a so-called integrating clutch for selectively coupling the prescribed two rotating elements in the planetary gear, that is, the sun gear and the ring gear, is provided.
When the integrating clutch couples the sun gear and the ring gear so as to integrate the whole planetary gear mechanism, the output torque of the engine is transmitted from the input shaft of the transmission to the planetary gear mechanism and the output shaft of the transmission through the continuously variable transmission mechanism. As a result, the gear ratio of the continuously variable transmission mechanism itself becomes the overall gear ratio of the transmission. On the other hand, the output torque of the continuously variable transmission mechanism is transmitted to the sun gear, and at the same time, the torque is transmitted from the input shaft to the carrier through the gear mechanism. In this case, the revolutions speed of the sun gear becomes smaller than that of the carrier as the gear ratio set by the continuously variable transmission mechanism increases. In other words, the revolution speed of the ring gear as the output revolution speed becomes larger than that of the carrier.
The transmission described in the above publication is capable of setting the following two modes: a mode (shift mode) in which the overall gear ratio of the transmission increases with increase in the gear ratio of the continuously variable transmission mechanism; and a mode (shift mode) in which the overall gear ratio of the transmission decreases with increase in the gear ratio of the continuously variable transmission mechanism.
The continuously variable transmission capable of continuously varying the gear ratio is advantageous in that, when used as a transmission of a vehicle driven by a power engine, the continuously variable transmission is capable of arbitrarily setting the revolution speed of the power engine, allowing improvement in power consumption. However, regarding the technology of cooperatively controlling a power engine and a transmission capable of changing the shift mode by using a continuously variable transmission mechanism and a planetary gear mechanism as described in the above publication, problems and means for solving them have not been sufficiently considered. Moreover, the above publication does not describe this type of control.